This invention relates to an automatic tool changer for use in a machine tool.
A conventional automatic tool changer includes a tool holder transfer means such as a chain. Plural tool holders are set in respective plural tool pots arranged in the chain. When a new tool holder is required to be exchanged for a used tool holder, a single changer having a swing arm is used in order to exchange directly the new holder set in the chain with the used holder set in the spindle.
On the other hand, in a conventional automatic tool changer, plural tools are selected to be used at a spindle in a so called random memory manner. If a certain tool holder is withdrawn from a tool pot for use in the spindle whereby the tool spot becomes empty, the used tool holder which has been withdrawn from the spindle is inserted in the empty tool pot. The tool holders are not returned to their original tool pots in the chain after use on the spindle.
In such a memory random type automatic tool changer, an operator can not easily check what tool holders are to be set in the many tool pots of the chain. Whenever each used tool holder is to be set in an empty tool pot, the type and address of the tool holder to be set in the specific tool pot must be memorized in a CNC unit for the purpose of its next use.
In this regard, an address fixed type automatic tool changer is preferable. Plural tool holders are returned to their original tool pots in the chain after used. The address of the tool holder does not change during operation so that it is not necessary to memorize the type of the tool holder to be set in the specific tool pot.
However, one defect of such a fixed address type automatic tool changer is that the exchange time is long. It takes a long time if a next or new tool holder in a tool pot which is far from a fixed exchange point is required to be exchanged for a used holder set in the spindle because the chain must transfer the next tool holder to the exchange point. Such a defect is increased as the number of tool holders set in the chain is increased.